This paper is the explanation provided by Richard S Courtney of why it is not possible for electricity from windfarms to be useful to the UK electricity grid. The explanation was presented at the 2004 Conference of "Groups Opposed to Windfarms in the UK." It includes explanation of why use of windfarms is expensive and increases pollution from electricity generation.

A companion presentation explained that windfarms (i.e., local assemblies of wind turbines) destroy the environment by covering it in concrete. And they are very efficient at swatting birds. These severe environmental costs may be worth suffering if windfarms were to provide cheap, clean, useful electricity. This presentation explains that

windfarms add a large, unnecessary cost to provision of electricity in the UK,

windfarms cannot provide any useful electricity to the UK grid at any time, and

the use of windfarms increases emissions from conventional power systems.*

Thermal power stations

Conventional power stations fission a material or burn a fuel to obtain heat that is used to boil water and superheat the resulting steam which is fed to the steam turbines (some power stations also use gas turbines in combination with steam turbines). The turbines drive turbogenerators that make electricity.

A power station takes days to start producing electricity from a cold start. Time is needed to boil the water, to superheat the steam, to warm all the components of the power station, and to spin the turbogenerators up to operating speed.

Each power station is designed to provide an output of electricity. It can only provide very little more or very little less than this output (i.e., a power station has a "low turndown ratio").

Electricity demand matching

Electricity is wanted all the time but the demand for electricity varies from hour to hour, day to day, and month to month. The electricity grid has to match the supply of electricity to the demand for it at all times. This is difficult because power stations cannot be switched on and off as demand varies.

The problem of matching electricity supply to varying demand is overcome by operating power stations in three modes called "base load," "generation," and "spinning standby."

Some power stations operate all the time providing electricity to the grid, and they are said to provide "base load."

Other power stations also operate all the time but do not provide electricity all the time. They burn (or fission) their fuel to boil water and superheat the resulting steam which is fed to the steam turbines that are thus kept hot and spinning all the time. Of course, they emit all the emissions from use of their fuel all the time. But some of this time they dump heat from their cooling towers instead of generating electricity, and they are then said to be operating "spinning standby."

One or more power stations can be instantly switched from spinning standby to provide electricity to match an increase to demand for electricity. It is said to be operating "generation" when it is providing electricity. Power stations are switched between spinning standby and generation as demand for electricity changes.

Thus the grid operator manages the system to match supply with demand for electricity by switching power stations between "generation" and "spinning standby."

Windfarm input to electricity

Windfarms only provide electricity when the wind is strong enough and not too strong. So, they suddenly provide electricity when the wind changes. The grid operator must match this changed supply of electricity to the existing demand for electricity. Of course, the grid operator achieves the match by switching a power station to spinning standby mode. That power station continues to operate in this mode so it can provide electricity when the windfarm stops supplying electricity because the wind has changed again.

Windfarms only force power stations to operate more spinning standby. They provide no useful electricity and make no reduction to emissions from power generation. Indeed, the windfarm is the true source of emissions from a power station operating spinning standby in support of the windfarm.

Windfarms have capital, maintenance and operating costs that add to the cost of electricity. These costs are their only contribution to electricity supply.

Power surges

A sudden, large addition to electricity in part of the grid is called a "power surge." It can overload a component of the grid with resulting widespread damage to the grid. For example, during the present year power surges have damaged components with resulting loss of power to the London Underground system, the city of Turin, and most of North America.

Wind turbines provide power when the wind is strong enough and not too strong. It is very difficult to predict the precise moment when a windfarm will start to provide electricity to the grid. And the wind can change over a large area. Hence, the presence of many windfarms in a locality causes power surges.

Denmark has many windfarms and so is subjected to power surges from them. The Danish grid manages this problem by dumping the electricity across its borders as a free gift to Denmark's neighbours. But some countries cannot do that. For this reason in December 2003 the Irish grid operator announced that he would accept no more electricity from windfarms onto the Irish grid. Additional windpower would be so unmanageable that grid failures would be inevitable.

The UK has a similar problem. The interconnector with France could not handle the dumping of a power surge. Hence, large use of windpower in the UK would cause damage to components of the UK grid and frequent power cuts throughout the UK.

Managing supply risk

As earlier explained, power stations operate spinning standby to match electricity demand to supply. In addition to this, other power stations operate spinning standby to manage risk of supply failures. There is a risk of failure of a base load power station or the transmission system from it. Such failures would cause power cuts in the absence of the additional spinning standby.

Windfarms only provide power when the wind is strong enough and not too strong. Hence, windfarms increase the risk of supply failures. Indeed, they give the certainty of supply failures when the wind is too strong or not strong enough. The increased risk of supply failures from windfarms is insignificant when there is small contribution of electricity to the grid from windfarms. All the output from the windfarms forces thermal power stations to operate spinning standby that can cope with the risk.

But the problem of managing the risk increases as the risk increases. Electricity is not wanted in the same amounts everywhere, and electricity is lost when it is transmitted over long distances. The additional management difficulties require additional spinning standby when the risk of supply failures is very large. Otherwise it would be impossible to match supply with demand throughout the grid when a large supply failure occurred.

Additional power stations must be built and operated on spinning standby (using their additional fuel and providing their additional emissions) to manage the increased risk of power cuts from supply failures when windpower contributes 20% or more of the potential electricity supply.

The construction of windfarms instead of power stations has caused these problems in California where scheduled voltage reductions are continuously provided around the State as an alternative method to manage the risk of power cuts from supply failures.

*"When plant is de-loaded to balance the system, it results in a significant proportion of deloaded plant which operates relatively inefficiently. ... Coal plant will be part-loaded such that the loss of a generating unit can swiftly be replaced by bringing other units on to full load. In addition to increased costs of holding reserve in this manner, it has been estimated that the entire benefit of reduced emissions from the renewables programme has been negated by the increased emissions from part-loaded plant under NETA." -- David Tolley (Head of Networks and Ancillary Services, Innogy (subsidiary of German energy consortium RWE)), keynote address, January 15, 2003, "NETA -- The Consequence," Institution of Mechanical Engineers. [NETA stands for New Electricity Trading Arrangements, the UK's deregulated power market.] --ED.